SBS and SIS belong to a styrene-based thermoplastic elastomer (also named styrenic block copolymers, SBCs) with properties of thermoplastic plastics and rubbers. For example, the SBCs are similar to rubber at room temperature due to their softness, toughness, and flexibility. Furthermore, the SBCs at high temperature are flowable and moldable. As with natural rubber and the synthetic rubber, the SBCs are classified as a third generation rubber. In the thermoplastic elastomer field, the SBCs' properties are mostly similar to that of rubber. In addition, the SBCs are the greatest yield thermoplastic elastomers in global. In recent years, SBCs include four types: styrene-butadiene-styrene block copolymer (SBS), styrene-isopentadiene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS), and styrene-ethylene-propylene-styrene block copolymer (SEPS). The SEBS and the SEPS are a hydrogenated SBS and SIS, respectively. The SEBS and the SEPS with excellent properties have a higher price (2 to 4 times) than that of the SBS and the SIS. The SBS is the most commonly SBC that is mass produced (over 70%), has the lowest-cost of the SBCs, and the more widely used product among the SBCs. The SBS is a triblock copolymer polymerized of styrene and butadiene. The SBS sir simultaneously has plastic and rubber properties, and is the greatest yield thermoplastic elastomer due to its excellent chemical resistance, excellent tensile strength, high surface friction coefficient, excellent low temperature properties, excellent electrical properties, and excellent processibility.
The polybutadiene segment of the SBS and the polyisopentadiene diene segment of the SIS include carbon-carbon double bonds. As such, the SBS and SIS have disadvantages such as low thermal resistance and low climate resistance (e.g. ozone resistance, UV resistance, and oxygen resistance). The disadvantages can be overcome by hydrogenating the carbon-carbon double bonds of the polybutadiene segment and the polyisopentadiene segment, thereby forming the SEBS (see Formula 1) and the SEPS (see Formula 2), respectively. The hydrogenated products SEBS and SEPS can be applied as engineering and medical materials due to better climate resistance and properties.

Accordingly, a novel method and corresponding catalyst for forming the SEBS and the SEPS is called for, e.g. selectively hydrogenating the carbon-carbon double bonding of the SBS and the SIS without hydrogenating the aromatic ring of the SBS and the SIS.